Multilayer medical balloon

ABSTRACT

An expandable medical balloon including an inner layer formed of a poly (ether-block-amide) copolymer and an outer layer formed of a polyamide, the expandable medical balloon having a burst strength of greater than 50,000 psi, and to methods of making and using the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/203,473, filed on Sep. 30, 2008, now issued as U.S. Pat. No.9,265,918, the disclosures of each incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of expandable medicalballoons, particularly those balloons employed for dilatation and forthe delivery of medical devices.

BACKGROUND OF THE INVENTION

Expandable medical balloons are employed in a variety of medicalprocedures including plain old balloon angioplasty (POBA) as well as fordelivery of medical devices to the treatment site such as stentdelivery.

Medical applications wherein a balloon is employed intraluminally suchas for POBA and stent delivery can be demanding applications due to theextremely small vessels, and the tortuous and long distances thecatheter may travel to the treatment site. For such applications, it istypically desirable that the balloon be thin walled, while maintaininghigh strength as most commonly measured by hoop strength or pressure atburst, be relatively inelastic, and have predictable inflationproperties.

Inelasticity is desirable to allow for easy control of the diameter, butsome elasticity is desirable to enable the surgeon to vary the balloon'sdiameter as required to treat individual lesions. Suitably, smallvariations in pressure should not cause wide variation in balloondiameter.

It can be difficult to achieve an excellent balance of properties with asingle polymer material. Therefore, a variety of polymer blends andmultiple layer polymer balloons have been developed over the years.

There remains a need in the art, however, for an expandable medicalballoon having an excellent balance of physical properties.

Without limiting the scope of the invention a brief summary of some ofthe claimed embodiments of the invention is set forth below. Additionaldetails of the summarized embodiments of the invention and/or additionalembodiments of the invention may be found in the Detailed Description ofthe Invention below.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to an expandable medicalballoon having at least two layers, an inner layer formed from a softer,elastic material, and an outer layer formed from a harder, less elasticmaterial.

In one aspect, the present invention relates to an expandable medicalballoon having an inner layer formed of a polymer material having aShore D hardness of about 25 to about 70 and an outer layer formed of apolymer material having a Rockwell hardness of about 60 to about 115,the expandable medical balloon having a burst strength of greater than45,000 psi, more suitably greater than 47,500 psi and most suitablygreater than 50,000 psi.

In one embodiment, the present invention relates to an expandablemedical balloon including an inner layer formed of a poly(ether-block-amide) copolymer and an outer layer formed of a polyamide,the expandable medical balloon having a burst strength of greater than45,000 psi, more suitably greater than 47,500 psi and most suitablygreater than 50,000 psi.

In another aspect, the present invention relates to a method of makingan expandable medical balloon, the method including forming a tubularparison, the tubular parison including an inner layer formed of a poly(ether-block-amide) copolymer and an outer layer formed from apolyamide, stretching said tubular parison at a stretch ratio of lessthan 4.0, radially expanding said tubular parison in a balloon mold andheat setting said balloon at a temperature of less than 150° C.

A synergistic increase in hoop strength has been exhibited with the duallayer balloons according to the invention.

These and other aspects, embodiments and advantages of the presentinvention will be apparent to those of ordinary skill in the art uponreview of the Detailed Description and Claims to follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table including a comparison of Rockwell hardness scale,Shore A hardness scale and Shore D hardness scale.

FIG. 2 is a longitudinal cross-section of a balloon having a dual-layercoating according to the invention.

FIG. 3 is a radial cross-section taken at section 3-3 in FIG. 2.

FIG. 4 is a longitudinal cross-section of a catheter assembly equippedwith a balloon according to the invention.

FIG. 5 is a side view of an expandable medical balloon with a stentdisposed thereon.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there aredescribed in detail herein specific embodiments of the invention. Thisdescription is an exemplification of the principles of the invention andis not intended to limit the invention to the particular embodimentsillustrated.

All published documents, including all US patent documents, mentionedanywhere in this application are hereby expressly incorporated herein byreference in their entirety. Any copending patent applications,mentioned anywhere in this application are also hereby expresslyincorporated herein by reference in their entirety.

The present invention relates to an expandable medical balloon having atleast two layers, an inner softer, more elastic layer, and an outerharder, less elastic layer. Suitably, the softer, more elastic innerlayer is formed from a material which also has a lower tensile set (seeASTM D412). This lower tensile set material forming the inner layerprovides for improved refoldability making withdrawal easier after aprocedure is complete.

Suitably, the shore D hardness of the inner layer is less than about75D, more suitably less than about 70D, with a range of about 25D toabout 75D, more suitably about 25D to about 70D. In some embodiments,the range is about 50D to about 75D, more suitably 50D to about 70D.

Suitably, the outer layer is harder than the inner layer. The outerlayer may have a Rockwell hardness between about 60 and about 115, moresuitably about 70 to about 115, and most suitably about 80 to about 115,although this range may vary. The Shore D hardness (ASTM D2240) of theouter layer is suitably greater than about 70D, more suitably greaterthan about 75D, and most suitably greater than about 80D. A comparisonof Shore A, Shore D and Rockwell hardness is shown in FIG. 1. FIG. 1 isreproduced fromhttp://www.calce.umd.edu/general/Facilities/Hardness_ad_.htm. As can beseen from the scale, nylon has a Shore D harness of 80 or greater and aRockwell hardness of greater than about 95. These numbers areapproximated from the scale.

In one embodiment, the inner layer is a poly (ether-block-amide) and theouter layer is nylon. In a preferred embodiment, the outer layer isnylon 12, formed from laurolactam. Nylon 12 is available fromDegussa-Hüls AG, North America under the tradename of Vestamid® L2101F.Degussa's national headquarters are located in Düsseldorf, Germany.Nylon 12 is available from a variety of polymer manufacturers. Poly(ether-block-amide copolymers are available from Arkema, North Americaunder the tradename of Pebax®. Arkema's headquarters are located inPhiladelphia, Pa. Specific grades of Pebax® useful herein include, butare not limited to, 6333 and 7033, with 7033 being preferred.

In a preferred embodiment, the balloon is formed with only the inner andouter layer as described herein. The inner layer provides at least 10%,and in some embodiments at least 20% of the burst strength of theballoon. Optionally, a lubricious coating may be disposed on the outerlayer. The lubricious coating does not provide structural integrity tothe balloon.

Shore D hardness values of PEBAX® 6333, 7033 and 7233 can be found athttp://www.pebax.com/sites/pebax/en/properties/mechanical_properties1.pageand are reproduced below in table 1. The standard used for thesemeasurements was ISO 868, which is equivalent to ASTM standard D2240.

TABLE 1 Shore A Shore D Hardness Hardness Pebax ® Grade InstantaneousAfter 15 s Instantaneous After 15 s 4033 90 89 41 34 5533 — — 54 50 6333— — 64 58 7033 — — 69 61 7233 — — 69 61

Other materials such as polyurethane elastomers, for example Tecothane®polyurethanes available from Noveon, Inc. in Cleveland, Ohio, findutility for use as the inner, softer layer. A specific example isTecothane® TT-1074A.

The resultant balloons suitably have a burst pressure of greater thanabout 400 psi, more suitably greater than about 450 psi, or a calculatedburst strength of greater than 45,000 psi, more suitably greater than47,500 psi and most suitably greater than 50,000 psi. Burst strength issometimes referred to in the art as hoop strength or radial tensilestrength.

The balloon may be formed using any suitable method known in the art. Insome embodiments, the method suitably includes forming a tubularparison, stretching the tubular parison, placing the balloon parison ina balloon mold, and forming a balloon by radially expanding the tubularparison into the balloon mold. The balloon is then heat set. Balloonforming with stretching and radial expansion is disclosed in U.S. Pat.Nos. 5,913,861, 5,643,279 and 5,948,345, and in commonly assigned U.S.Pat. Nos. 6,946,092 and 7,1010,597, each of which is incorporated byreference herein in its entirety.

The tubular parison may be formed using coextrusion techniques. Thetubular parison may have two layers including a soft inner layer and aharder outer layer, or may have alternating soft and hard layers. Forexample, layers 1, 3 and 5 (with 1 being the innermost layer of theballoon) are formed from the flexible, softer layer, while layers 2, 4and 6 are formed of the harder, higher strength polymer material.

Alternatively, the softer, more flexible inner layer can be coatedeither on the balloon parison, or on the balloon itself after it hasbeen formed from the balloon parison. Coating can be accomplished out ofa solvent or solvent blend. The coating can be injected into the tubularparison or balloon, for example.

In some embodiments, it may be desirable for the waist portion of theballoon to be formed of only a single layer. The waist can be maskedwith an inserted tube, or cleaned after application of the coating.

Suitably, the tubular parison is axially (longitudinally) stretchedusing a stretching ratio of less than 4.0X where X is the startinglength of the tubular parison. In one specific embodiment, the methodincludes stretching the balloon parison at a ratio of 3.50X wherein X isthe starting length of the tubular parison.

At a stretch ratio of significantly more than this, for example, at astretch ratio of 4.25, a decrease in balloon burst pressure of more than20% was observed, and the corresponding decrease in calculated burststrength was greater than 10%.

The balloon can then be formed from the tubular parison using anysuitable technique including molding. Using molding techniques, thetubular parison can be placed into a mold and radially expanded. Moldingpressures may range between about 500 psi and about 600 psi.

Suitably, the balloon is heat set at a temperature of about 150° C. orless. In some embodiments, the heat set temperature is about 125° C. orless. In a specific embodiment, the balloon is heat set at 120° C. Ithas been found that using a temperature for heat setting that issignificantly higher than this, negatively impacts the ultimate burststrength of the balloon. For example, at a heat set temperature of 140°C., the burst pressure was found to decrease by more than 15% over thesame balloon formed at 120° C., and the corresponding decrease in burststrength was more than 10%.

The resultant balloons, for example, those used for cardiovascularprocedures, suitably have a wall thickness of between about 10 micronsand about 30 microns, and even more suitably about 10 microns to about20 microns.

Turning now to the figures, FIG. 2 is a longitudinal cross-sectionalrepresentation of a balloon 10 according to the invention. Balloon 10 isshown with dual layers having an inner layer 12 and an outer layer 14 inaccordance with the invention. FIG. 3 is a radial cross-section taken atsection 3-3 in FIG. 2.

The balloon can further include a lubricious coating (not shown). Thelubricious coating may be applied to the balloon waists 16, 18, ballooncones, 17, 19 and balloon body 21, or any portion thereof. Suitably,lubricious coatings are applied at a thickness of about 0.1 microns toabout 5.0 microns, more suitably about 0.5 microns to about 2.0 microns.

Any suitable lubricious material may be employed in the lubriciouscoating. Such lubricious coatings are known in the art. Examples ofmaterials that can be used in the lubricious coatings include boththermoplastic and thermoset materials. The lubricious polymers can beeither hydrophobic or hydrophilic. Hydrophilic materials are oftenpreferred because they are typically more biocompatible. Lubriciouscoatings are disclosed in commonly assigned U.S. Pat. No. 5,509,899, theentire content of which is incorporated by reference herein.

Interpenetrating polymer networks can also be employed. These materialsare described, for example, in commonly assigned U.S. Pat. No.5,693,034, the entire content of which is incorporated by referenceherein.

Coatings for the controlled delivery of therapeutic agents may also beoptionally added.

FIG. 4 is a longitudinal cross-section of a catheter assembly 20equipped with a balloon 10 according to the invention. Catheter assembly20 is a dual-lumen catheter having an inner shaft 22 and an outer shaft24. Inner shaft 22 has an inner surface 23 defining a guide wire lumen26. Guide wire 28 is shown disposed within lumen 26.

Proximal waist 16 of balloon 10 is disposed about the distal end ofouter shaft 24 and distal waist 18 of balloon 10 is disposed about thedistal end of inner shaft 22.

The assembly may further incorporate a stent 30 disposed about balloon10 as shown in FIG. 5. In the case of stent delivery application, it maybe desirable to have a lubricious coating applied to only the waistportions 16, 18, cone portions 17, 19, or a combination of the waist andcone portions.

The balloons described herein may be employed in any of a variety ofmedical procedures including, but not limited to, angioplasty (PTCA)procedures, for delivery of medical devices such as stents (SDS),genito-urinary procedures, biliary procedures, neurological procedures,peripheral vascular procedures, renal procedures, etc.

The following non-limiting examples further illustrate some aspects ofthe present invention.

EXAMPLES Example 1

Vestamid L2101F and Pebax 7033 were coextruded axially into the tubingof ID 0.0196 by OD 0.0348 inches. The outer layer was Vestamid L2101Fwith 70% of cross section area (material ratio) and the inner layer wasPebax 7033 with 30% of cross section area (material ratio). The tube wasstretched at the speed of 50 mm/sec at 45° C. temperature with theinside pressure of 400 psi at a stretch ratio of 3.50. The stretchedtube was inserted into a 0.1260 inch balloon mold (inner diameter or IDor balloon mold), and a balloon was formed at 95° C. and heat set rightafter formation at 120° C. for 1 minute. The balloon forming pressurewas 500 psi.

The average balloon burst at 465 psi (31.6 atm) (burst pressure) withthe average double wall thickness of 0.00114 inches. The averagedistention of the balloon was 5.8% at 6/16 atm range. The averageballoon diameter was 3.3024 mm.

Burst strength is calculated using the following formula:Strength=P×D/2twhere P=internal pressure when the balloon bursts (kg/cm²) (psi); D isthe exterior diameter (mm) of the balloon when a pressure of 6.2 kg/cm²(88 psi) is applied; and t is the wall thickness of the portion of theballoon with the larger exterior diameter.

The calculated burst strength was 53,033 psi.

Hoop ratio can also be calculated using the following formula:ID(BM)/(OD−ID)×(ln(OD/ID)=Hoop RatioID (BM) is the inner diameter of the balloon mold and OD and ID are theouter diameter and the inner diameter of the tubular parisonrespectively.

For example 1, the hoop ratio is 4.758.

Comparative Example A

For comparison, the same material ratio was used as described in theabove example but with opposite material arrangement, i.e., the softermaterial outside. In this example, Vestamid L2101F is inner layer (70%in material ratio) and Pebax 7033 was outer layer (30% in the ratio).The same dimension tubing was extruded and the same size balloon wasformed per balloon forming process described in the above example.

The tube was axially stretched at the speed of 50 mm/sec at 45° C.temperature with the inside pressure of 400 psi at a stretch ratio of3.50. The stretch ratio is based on the starting length of the tube, X.In other words, the stretch ratio is 3.50X. The stretched tube wasinserted into a 0.1260 inches balloon mold, and a balloon was formed at95° C. and heated set right after formed at 120° C. for 1 minute. Theballoon forming pressure was 500 psi.

The balloon burst at 386 psi (26.3 atm, in average) (burst pressure)with the average double wall thickness of 0.00108 inches. The distentionof the balloon was 6.7% at 6/16 atm range. The average balloon diameterwas 3.360 mm.

The calculated burst strength was 47,280 psi.

Comparative Example B

The same inner and outer layers were employed as in Example 1 but adifferent tubing stretch ratio was employed.

The tube was axially stretched at the speed of 50 mm/sec at 45° C.temperature with the inside pressure of 400 psi at stretch ratio of4.25. The stretched tube was inserted into a 0.1260 inches balloon mold,and a balloon was formed at 95° C. and heat set right after formed at120° C. for 1 minute. The balloon forming pressure was 600 psi.

The average balloon burst at 366 psi (24.9 atm) with the average doublewall thickness of 0.00103 inches. The average distention of the balloonwas 6.0% at 6/16 atm range. The average balloon diameter was 3.3505 mm.

The calculated burst strength was 46,872 psi.

Comparative Example C

The same inner and outer layers were employed as in Example 1 but adifferent heat set temperature was employed.

The tube was stretched at the speed of 50 mm/sec at 45° C. temperaturewith the inside pressure of 400 psi at stretch ratio of 3.50 (the samestretch ratio as in example 1). The stretched tube was inserted into a0.1260 inches balloon mold, and a balloon was formed at 95° C. and heatset right after formed at 140° C. for 1 minute. The balloon formingpressure was 500 psi.

The average balloon burst at 391 psi (26.6 atm) (burst pressure) withthe average double wall thickness of 0.00113 inches. The averagedistention of the balloon was 6.8% at 6/16 atm range. The averageballoon diameter was 3.362 mm.

The calculated burst strength was 45,802 psi.

Increasing the heat set temperature to 140° C., was therefore found tohave a negative impact on the burst pressure wherein a decrease ofgreater than 15% was seen over example 1. The corresponding drop incalculated burst strength was found to be greater than 10% over example1.

The above disclosure is intended to be illustrative and not exhaustive.This description will suggest many variations and alternatives to one ofordinary skill in this art. The various elements shown in the individualfigures and described above may be combined or modified for combinationas desired.

The invention claimed is:
 1. A method of making an expandable medicalballoon, the expandable medical balloon having an inner layer formed ofa poly(ether block amide) copolymer; and an outer layer formed of apolyamide; the method comprising: forming a tubular parison, the tubularparison comprising the inner layer formed of a poly(ether-block-amide)copolymer and the outer layer formed from a polyamide; longitudinallystretching the tubular parison at a stretch ratio of less than 4.0; andradially expanding the tubular parison in a balloon mold to form theexpandable medical balloon.
 2. The method of claim 1 further comprisingheat setting said balloon at a temperature of less than about 150° C. 3.The method of claim 2 wherein said heat set temperature is about 120° C.4. The method of claim 1 wherein said stretch ratio is about 3.5 orless.
 5. The method of claim 1 wherein said polyamide is formed fromlaurolactam.
 6. The method of claim 1 wherein said balloon mold is at apressure of about 500 psi to about 600 psi.
 7. The method of claim 1wherein a radial cross-section of said tubular parison comprises amaterial ratio of about 70% to about 30% based on the outer layer to theinner layer.
 8. The method of claim 1 wherein the resultant expandablemedical balloon has a burst strength of 45,000 psi or more.
 9. Themethod of claim 1 wherein the inner layer has a Shore D hardness ofabout 50D to about 70D.
 10. The method of claim 1 wherein the outerlayer has a Rockwell hardness of about 80 to about
 115. 11. The methodof claim 1 further comprising the step of applying a lubricious coatingto at least a portion of said outer layer.
 12. The method of claim 11wherein said lubricious coating is applied by a method selected from thegroup consisting of dipping, spraying, brushing, sponge coating, and padprinting.
 13. A method of making an expandable medical balloon, theexpandable medical balloon having an inner layer formed of an elastomer;and an outer layer formed of a non-elastomer; the method comprising:forming a tubular parison, the tubular parison comprising the innerlayer from an elastomer and the outer layer formed from a non-elastomer;longitudinally stretching the tubular parison at a stretch ratio of lessthan 4.0; and radially expanding the tubular parison in a balloon moldto form the expandable medical balloon.
 14. The method of claim 13further comprising heat setting said balloon at a temperature of lessthan about 150° C.
 15. The method of claim 13 wherein said heat settemperature was about 120° C.
 16. The method of claim 13 wherein saidstretch ratio is about 3.5 or less.
 17. The method of claim 15 whereinthe outer layer has a Rockwell hardness between about 70 and about 115and the inner layer has a Shore D hardness of about 50D to about 75D.18. The method of claim 13 wherein the outer layer has a Shore D harnessof 80D or greater or a Rockwell hardness of greater than about
 95. 19.The method of claim 13 wherein a radial cross-section of said tubularparison comprises a material ratio of about 70% to about 30% based onthe outer layer to the inner layer.
 20. The method of claim 13 whereinthe resultant expandable medical balloon has a burst strength of 45,000psi or more.